Electro-hydraulic pulse motor

ABSTRACT

This disclosure relates to an improved electro-hydraulic pulse motor having an arrangement wherein novel stop means are provided for screw-nut coupling which couples the four-way pilot valve part to the hydraulic motor part while providing a feedback loop in the operation of the electro-hydraulic pulse motor so that the axial motion of a valve spool of the four-way pilot valve part which motion is driven by the electric pulse motor part, is properly restricted so as not to fail in delivering control action to the hydraulic line formed in the electro-hydraulic pulse motor.

United States Patent Inaba et al.

[ Aug. 14, 1973 ELECTRO-HYDRAULIC PULSE MOTOR inventors: Seiuemon lnaba, Kawasaki; Kohei Ito, Fujisawa; Kanryo Shimizu, Kawasaki; Youichi Amemiya, Tokyo. all of Japan Assignee: Fujitsu Limited, Kawasaki-shi,

Kanagaiva-ken, Japan Filed: iiZEf lifi 97l-f Appl. No.2 207,105

Foreign Application Priority Data Dec, 26, 1970 Japan 45/131958 (utility model) US. Cl. 91/39, 15l/10 Int. Cl. F151) 21/00 Field of Search 91/486, 375, 380,

- References Cited UNITED STATES PATENTS 4/1955 Ruppert... 9/1970 Tomita.....

3,296,936 1/1967 Wess et a1 91/380 3,621,762 11/1971 3,596,569 8/1971 Wisbey 91/380 Primary Examiner-William L. Freeh Assistant Examiner-Gregory Lalointe Att0mey-A1an Ratner et a1.

[57] ABSTRACT This disclosure relates to an improved electrohydraulic pulse motor having an arrangement wherein novel stop means are provided for screw-nut coupling which couples the four-way pilot valve part to the hydraulic motor part while providing a feedback loop in the operation of the electro-hydraulic pulse motor so that the axial motion of a valve spool of the four-way pilot valve part which motion is driven by the electric pulse motor part, is properly restricted so as not to fail in delivering control action to the hydraulic line formed in the electro-hydraulic pulse motor.

1 Claim, 3 Drawing Figures I 1 ELECTROJIYDRAULIC PULSE MOTOR The present invention relates to an improvement of an electro-hydraulic pulse motor and more particularly relates to an improved internal structure of the feedback screw-nut coupling of an electro-hydraulic pulse motor.

The conventional electro-hydraulic pulse motor has an arrangement in which the principal parts thereof consisting of an electric pulse motor, a rotary-type four-way pilot valve and an axial piston hydraulic motor, are operatively coupled to each other by a reduction gear and a screw-nut coupling having feedback operation and forming a feedback loop in the hydraulic line of the electro-hydraulic pulse motor.

The above-mentioned conventional electrohydraulic pulse 'motor works on an operational principle as disclosed below.

A predetermined amount of rotation of the electric pulse motor shaft in response to the impression of an electric pulse or of electric pulse train to the input of the electric pulse motor, is transmitted to the valve spool of the four-way pilot valve part by means of the reduction gear so as to cause rotation of the valve spool. The rotation of the valve spool is transformed into an axial shift of the valve spool by the abovementioned screw-nut coupling and the axial shift of the valve spool from the initial neutral position opens an oil supply port provided for the four-way pilot valve part so as to introduce hydraulic fluid from the fluid power source actuating the hydraulic motor part to provide a large torque on theshaft of the hydraulic motor part which is also the output shaft of the electro-hydraulic pulse motor, the output being used for driving, e.g., a machine on the one hand. n the other hand, the output rotation of the hydraulic motor part, restores the valve spool of the four-way pilot valve part to the neutral position thereof, where the hydraulic line is blocked, again by means of the screw-nut coupling, and one cycle of operation of the. electro-hydraulic'pulse motor is finished with respect to a pulse input impressed thereto.

However, in this conventional arrangement of the electro-hydraulic pulse motor, it oftens occurs an accidentally that the valve spool is not restored to the neutral position thereof and fails to deliver control action to the hydraulic line, and therefore, continuously uncontrolled torque is produced on the output shaft of the electro-hydraulic pulse motor. This uncontrolled torque breaks down the machine which is driven by the electro-hydraulic pulse motor. I

The object of the present invention is to provide an electro-hydraulic pulse motor provided with an internal structure capable of eliminating the above-mentioned drawback.

Further features and advantages of the present invention will be apparent from the ensuing description with reference to the accompanying drawings wherein:

FIG. I is a sectional view of an electro-hydraulic pulse motor;

FIG. 2 is a partial view of a stopping sturcture of the valve spooldevised generally and conventionally;

FIG. 3 is a partially sectional view of a stopping structure of the valve spool provided in an electrohydraulic pulse motor according to the present invention.

FIG. 1 shows the overall arrangement of an electrohydraulic pulse motor, input I is arranged at electric pulse motor part 2, and an electric pulse signal is impressed to the input 1. The electric pulse motor part 2 is coupled to a rotary type four way pilot valve part 4 having a sleeve 7 and valve spool 5 by means of a reduction gear 3 provided between one end portion of the spool 5 and the shaft of the electric pulse motor part 2.

The. rotary type four way pilot valve part 4 is also coupled to an axial piston type hydraulic motor part 6 by means of a feedback screw-nut coupling formed by a screw 9 threaded at one end portion of the valve spool 5 and a nut 8 threaded at an inner end portion of shaft 6' of the hydraulic motor part 6. Reference numerals Ill and 12 shown in FIG. I are oil supply and return port connected to the ports of the four way pilot erally and conventionally devised to restrict the amount of axial shift of the valve spool 5 to a predetermined value in order to avoid disconnection of the coupling between screw 7 and nut 8. That is, stop projections 13 and 13' are made at the end walls of screw nut 8 and the inside of the casing of an electro-hydraulic pulse motor.

However, when the rotational motion of the valve spool 5 in response to an operation of electric pulse motor part 2 is converted into an axial motion by means of the screw-nut coupling, an extremely large thrust force is produced on the valve spool 5 and accordingly, large friction force is produced at the contact points when the valve spool 5 comes in contact with the stop projection 13 or 13' under the large thrust force. As a result of this, there often occurs an accident wherein the valve spool 5 rotates with the shaft 6' of hydraulic motor part 6 in a unitary condition through over tight contact of the spool 5 and projection 13 of nut 8 when the hydraulic motor part 6 is actauted by I hydraulic fluid force introduced by the four way pilot .valve part 4 and therefore, the valve spool 5 is prevented from being restored to the initial neutral position thereof.

In accordance with the feature of the present invention illustrated, hereinafter, with reference to FIG. 3, means to properly restrict the axial motion of the valve spool 5 is provided so that the above-mentioned drawback can be completely eliminated.

Referring now to FIG. 3 which illustrates an embodiment of the present invention, a stop member It! is disposed at a side wall portion of nut 8, whilevalve spool 5' is provided with'a channel 15 between screw 9 and stem portion 16, which co-operates with stop member 10 so as to restrict the shifting motion of spool 5' shown by an arrow in FIG. 3, relative to shaft 6' of hydraulic motor part 6, to a predetermined value. That is, the end I9 of valve spool 5' does not make any contact with the end face 14 of nut 8. Also, as shown in FIG. 3, the channel 15 has a predetermined amount of axial width corresponding to the predetermined amount of shift of valve spool 5' and is formed in a skewed state at the same skewing angle as the lead angle of screw 7. In accordance with this skewed state of channel 15, the rotationally shifting valve spool 5' comes into contact with stop member 10 embedded in the side wall'portion of nut 8, at both end portions 17 and 18 of valve spool 5 but without being affected by the above-mentioned large thrust force produced on valve spool 5.

Therefore, friction force which conventionally causes a seized condition at the contact portion of screw 7 and nut 8, is not produced at either end portions 17 and 18 of valve spool when the valve spool 5' comes into contact with stop member 10.

The stop member is arranged so as to be rigidly embedded in nut 8 as shown in FIG. 3, so that it can sufficiently bear the load given by valve spool 5.

Therefore, it is obvious that in accordance with the above-mentioned improved structure, the electrohydraulic pulse motor of the present invention can never be subject to the above-mentioned accident.

The present invention is illustrated in accordance with a preferred embodiment. However, the'structure is of course applicable to the case where the screw 7 is formed at the end of shaft 6' of the hydraulic motor part 6 and nut 8 is formed at the end of valve spool 5 of the four-way pilot valve part 4.

We claim:

1. An electro-hydraulic pulse motor comprising an electric pulse motor;

a rotary pilot valve including a sleeve and a valve spool inserted in the sleeve to be axially slideable with respect to said sleeve and operatively associated with the electric pulse motor;

an hydraulic motor rotated by supply of a pressure oil via the rotary valve; feedback means constituted by a coupled screw and nut threadedly engaged with each other, one being connected to the valve spool and the other being connected to the hydraulic motor or the electric pulse motor and;

stop means comprising a channel formed in said screw, stop ends fonned in opposing ends of the channel, and a stop member disposed in said nut radially projecting into the channel whereby relative rotational motion between the screw and the nut as well as axial movement of the valve spool is restricted to a predetermined magnitude due to contact of the stop member and the respective stop ends of the channel. 

1. An electro-hydraulic pulse motor comprising an electric pulse motor; a rotary pilot valve including a sleeve and a valve spool inserted in the sleeve to be axially slideable with respect to said sleeve and operatively associated with the electric pulse motor; an hydraulic motor rotated by supply of a pressure oil via the rotary valve; feedback means constituted by a coupled screw and nut threadedly engaged with each other, one being connected to the valve spool and the other being connected to the hydraulic motor or the electric pulse motor and; stop means comprising a channel formed in said screw, stop ends formed in opposing ends of the channel, and a stop member disposed in said nut radially projecting into the channel whereby relative rotational motion between the screw and the nut as well as axial movement of the valve spool is restricted to a predetermined magnitude due to contact of the stop member and the respective stop ends of the channel. 